Several possibilities of resisting such forces of withdrawable unit systems are known in the state of the art. WO 2004/040726 A2 discloses a device for fixing a circuit breaker in an insertion rack. The device includes at least one arresting unit which is connected to the insertion rack and belongs to the power circuit breaker. The arresting unit is connected to a control rod which is movable arranged on the insertion rack in such a way that it is displaceable from a locking position to an unlocking position and vice-versa. The control rod interacts with a system which moves the power circuit breaker in relation to the insertion rack. The device also includes a release device which can be displaced from the locking position of the control rod to the releasing position thereof and vice-versa by way of the power circuit breaker.
U.S. Pat. No. 5,837,949 discloses a withdrawable unit, which includes a movement bracket assembly adapted for mounting to a circuit breaker connecting apparatus, a guide assembly adapted for mounting to a circuit breaker unit, and a drive assembly adapted for mounting the bracket assembly and for causing the guide assembly to move with respect to the bracket assembly.
This withdrawable unit is able to move the circuit breaker from a position, where the main contacts and the usually existing auxiliary contacts for control and information signals are closed, i.e. the operating position, to a test position, i.e. a position, where only the auxiliary contacts are closed, whilst the main contacts are disconnected, and further to a withdrawn position, where all contacts are disconnected, and vice-versa. For the linear movement of the circuit breaker, a side wall of the withdrawable unit contains a spindle drive, which is drivable via a drive tool, insertable from the front of the withdrawable unit.
DE 92 12 149 U1 also discloses a device for fixing a power circuit breaker provided with a partition plate and in which a blocking lever, which is fixed on the withdrawable unit, can be brought by hand into a latched or an unlatched position, and the power circuit breaker is fixed in the latched position by way of a locking hook. The locking hook prevents a possible tipping movement of the power circuit breaker.
Analogous locking for a withdrawable unit equipped with a device for inserting the power circuit breaker does not, however, have to be undertaken by hand, which would then have the hidden risk of locking being forgotten.
The necessity of access to the control elements cause openings in the walls of the withdrawable unit. Therefore such withdrawable units do not pass superior types of protection, like protection against dust or water.